Note: Descriptions are shown in the official language in which they were submitted.
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DOCKET NO.: 10323-9002
LAYER PALLETIZING GRIPPER WITH VACUUM ASSIST
Field of the Invention
The present invention relates to mechanisms used to grasp boxes and other
types of
containers. More specifically, the present invention relates to a robotic end
effector used to
handle containers wrapped in plastic and similar types of packaging material.
Background of the Invention
Robots are used in a wide variety of applications. Commonly, they are used in
welding
and cutting operations. They are also use in material handling applications.
One typical material
handling application involves the movement of boxes filled with product from
an accumulation
station of a processing line to a pallet for shipping to distributors and
customers. This process is
referred to as "palletizing."
Generally, palletizing is accomplished using friction-grip claws and hands.
Mechanical
claws, hands and other devices that grasp and manipulate desired items are
generically referred
to as "end effectors." Friction-type end effectors usually grasp a box between
two claws. The
friction between the surface of the box and the claws is generally sufficient
to hold the box in
place until the claws are released. Often, even multiple boxes in a single
layer can be grasped in
this manner. Depending on the number, weight, and size of boxes to be grasped,
auxiliary
vacuum cups are sometimes used with claws to enhance the grip on the boxes and
prevent boxes
from falling from the grasp of the end effector. As can be appreciated, if one
box slips from the
end effector, generally all or multiple boxes will also fall out of its grip.
Of course, to the extent
fall-out can be prevented, and entire layers of boxes grasped, palletizing
speed can be increased.
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While systems of the type described are useful, particular problems arise when
handling
boxes wrapped with plastic and similar packaging material. First, the
packaging material
wrapped around such boxes usually has a low coefficient of friction. This
makes grasping such
boxes with claws alone difficult, because sufficient friction can not be
achieved between the
surface of the packaging and the claws. Increasing the compression force of
the claws to create
sufficient grip is generally not practical as the increased force tends to
damage the boxes.
Second, if conventional vacuum assistance is used, the packaging on the boxes
tends to "tent."
Tenting occurs because the vacuum seal formed with a wrapped box is between
the vacuum
device and the packaging material, not between the vacuum device and the box
itself. Thus, as a
wrapped box is raised by the robot, the packaging material stretches and pulls
away from the box
and the stretched material acts like a pendulum connection between the vacuum
device and the
box in the packaging. When the robot moves, the box tends to swing and in many
cases that
motion will break the vacuum seal causing the box to drop from the end
effector.
In an attempt to solve some of these problems, large vacuum-type end effectors
were
tested to determine their ability to grasp entire layers of boxes. However,
generating sufficient
vacuum suction to lift an entire layer of boxes requires vacuum generators of
impractical size,
weight, and cost.
Accordingly, there is a need for an end effector that overcomes the problems
of present
systems and that can handle items wrapped in packaging material.
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Summary of the Invention
The present invention provides an end effector that overcomes the problems of
previous
end effectors used to grasp boxes and similar containers wrapped in packaging
material. The
present invention includes an end effector having a main body and two hands.
The end effector
is designed to be used with an industrial robot which is controlled by a
processor or
programmable computer. The~hands are positioned opposite one another and
coupled to the
main body. Each hand is powered by an actuator and operable to move between a
first, retracted
position and a second, extended position. Each hand has a plurality of
fingers. In one
embodiment each hand has numerous, relatively thin fingers that are designed
to flex slightly
when gripping a load. These fingers are aligned at an angle with respect to a
vertical plane. In
another embodiment of the invention, each hand has relatively few fingers and
each finger is
relatively rigid. Further, some of the rigid fingers may be removed from the
hands and others
may be powered by an actuator to provide additional grasping and release
capabilities. The
fingers may also be shaped or contoured with cut outs to provide clearance
while grasping
various types of loads. In both embodiments, the fingers may be covered with
rubber or similar
materials to enhance the coefficient of friction between the wrapped boxes and
the fingers.
Regardless of the type of fingers used, to pick up a load the end effector is
moved into
position by the robot over a layer of boxes and the hands are closed around
it. A synchronization
mechanism coupled to the first and second hands helps ensure that the hands
open and close at a
uniform rate. A vacuum assist system is then engaged to help maintain the grip
on the layer of
boxes. The vacuum assist system includes two vacuum plate assemblies. A first
vacuum plate
assembly is coupled to the main body and positioned between the two hands. A
second vacuum
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plate assembly is similarly coupled to the main body and positioned opposite
the first vacuum
assembly.
Each of the two vacuum plate assemblies includes an actuator mounted on the
main body,
a vacuum plate connected to the actuator, and a set of vacuum devices mounted
on the underside
of the vacuum plate. The first end of a third set of vacuum devices may be
coupled to one of the
vacuum plates. The second end of the third set of vacuum devices may be
coupled to the other
vacuum plate such that the three sets of vacuum devices are aligned in a row.
The row of
vacuum devices is movable by means of the two actuators between a first, upper
position and a
second, lower position. Once the hands grasp a layer of boxes, the vacuum
devices are lowered
to engage the seam between adjacent boxes and provide additional gripping,
i.e., a "vacuum
assist."
To provide additional functionality for the palletizing of boxes, the present
invention may
include a slip sheet gripper. In one embodiment of the invention, a first slip
sheet gripper
assembly is coupled to the first vacuum plate, and a second slip sheet gripper
assembly coupled
to the second vacuum plate. The slip sheet gripper assemblies are designed to
grasp bottom, slip,
and cap sheets that may be inserted underneath, between, and on top of layers
of boxes as they
are placed on a pallet.
These are just some of the features and advantages of the present invention.
Many others
will become apparent by reference to the detailed description of the invention
taken in
combination with the accompanying drawings.
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Brief Description of the Drawings
FIG. 1 is a perspective view of one embodiment of an end effector of the
present
invention mounted on a robot (shown in phantom).
FIG. 2 is a top, perspective view of the end effector of FIG. 1.
FIG. 3 is an end view of the end effector of FIG. 1.
FIG. 4. is a bottom view of the end effector of FIG. 1 showing the hands
thereof in
extended positions.
FIG. 5 is a bottom view of the end effector of FIG. 1 showing the hands
thereof in a
retracted position.
FIG. 6 is a perspective view of another embodiment of the end effector of the
present
invention.
FIG. 7 is a perspective, end view of the end effector of FIG. 6.
FIG. 8 is a bottom view of the end effector of FIG. 6.
FIG. 9 is a side, perspective view of a toggle mechanism used in the end
effector of FIG.
6 showing a movable finger in a closed position.
FIG. 10 is a side, perspective view of the toggle mechanism showing the finger
in an
open position.
FIG. 11 is a side perspective view of the present invention grasping a layer
of boxes.
FIG. 12 is a perspective view of a stack of differently sized rows of boxes.
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Detailed Description
An end effector 20 constructed in accordance with the teachings of the present
invention
is shown in FIG. 1. The end effector 20 is designed to be mounted on an
industrial robot 22
(shown in phantom) of conventional design controlled by a processor 24 or a
similar device such
as a programmable computer. The robot 22 has a robot arm 25 and a wrist 26. As
best seen by
reference to FIGS. 2-S, the end effector 20 has a main body 28 with a first
side 29A, a second
side 29B, a third side 29C, a fourth side 29D, and a mounting bracket or wrist
adapter 30, which
is designed to be coupled to the wrist 26 of the robot 22. A first hand 40 is
coupled to the first
side 29A of the main body 28. The hand 40 includes a main support 41 and two
rods 43 and 44.
The rods 43 and 44 are inserted into pillow box bearings 45, 46, 47, and 48,
as shown. A first
main actuator 50, such as a fluid-activated linear actuator, is positioned
between the bearings and
mounted on the main body 28. The actuator 50 is coupled to the main support 41
through a
driving rod 52 and operable to move the hand between a first, retracted
position H1A and a
second, extended position H1B (FIGS. 4 and 5).
The hand 40 has a plurality of fingers 60. Each finger 60 consists of a plate
of relatively
rigid, yet slightly flexible material and preferably is made from stainless
steel about 1/8 of an
inch thick. The plates that form each finger 60 are preferably angled at an
angle A of about three
degrees to provide additional gripping force when grasping a layer of items
(FIG. 3). Each
finger may be coated with a layer of rubber or other material such as high-
strength, natural latex
rubber that exhibits stickiness. It has been found that rubber having a
durometer of about 40 is
useful for the purposes of the present invention.
A second hand 70 is coupled to the third side 29C of the main body 28,
opposite the hand
40. The second hand 70 is driven by an actuator 71 and movable between a
first, retracted
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position H2A and a second, extended position HzB (FIGS. 4 and 5). The second
hand 70 is
essentially the same as the hand 40. Thus, the remaining details of its
construction and operation
will not be discussed herein.
Motion of the hands 40 and 70 between their retracted and extended positions
is
synchronized by a linkage assembly 75 (FIG. 4). The linkage assembly 75
includes a lever arm
76 pivotally mounted on the bottom of the main body 28, a first arm 77 coupled
to the first hand
40 and a second arm 78 coupled to the second hand 70. If the actuators 50 and
71 drive the
hands 40 and 70 at unequal rates, the linkage assembly 75 brakes the motion of
the faster
actuator and transfers the motion to the slower moving hand to equalize their
rates of movement.
The operating principle of the hands is the same as a mechanical claw. The two
hands close
around a layer of boxes (such as the layer 79 in FIG. 1) to frictionally
engage them. However,
this frictional grip is not sufficient in most cases to grasp items wrapped in
packaging material.
Therefore, the present invention also employs a vacuum assist system to
maintain a proper grip
on the items.
Part of the vacuum assist system is a first vacuum assembly bracket 80 which
is mounted
on the second side 29B of the main body 28 (FIG.2). A first vacuum assembly
actuator 82 is
coupled to the bracket 80. The first vacuum assembly actuator 82 is coupled to
a first vacuum
plate 84 and is operable to drive the plate between a first, upper position PU
and a second, lower
position PL. A first set of vacuum devices 86 is mounted on the bottom of the
first vacuum plate
84 in a centrally positioned location along a horizontal axis (FIG. 4). The
vacuum devices 86,
like the other vacuum devices described herein may be conventional vacuum cups
powered by
Venturi-type vacuum generators (such as a generator 87) supplied with air
through a valve
manifold, such as one of the valve manifolds 88 or 89. Since the operation of
such vacuum
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devices is known , the connection of vacuum lines and other details of the
vacuum devices are
not provided here.
With continuing reference to FIGS. 2, 3, and 4, a second vacuum assembly
bracket 90 is
mounted on the fourth side 29D of the main body 28. A second vacuum assembly
actuator 92 is
mounted on the bracket 90 and is coupled to a second vacuum plate 94. The
actuator 92 is
operable to drive the plate between the positions PU and PL. A second set of
vacuum devices 96
is mounted on the bottom of the second vacuum plate in a central position
along a horizontal
axis. The set of vacuum devices 96 is substantially the same as the set of
devices 86 and may
also be coupled to one of the valve manifolds discussed above. A third set of
vacuum devices
100 is coupled to the first and the second vacuum plates and is linearly
aligned with each set 86
and 96. The motion of the first and second vacuum actuators 82 and 92 is
coordinated so that the
two plates 84 and 94 are moved together between the positions PU and PL, as
desired.
The hands 40 and 70 are used in combination with the sets of vacuum devices to
grasp a
layer of wrapped boxes. As best illustrated by FIG. 11, the end effector 20 is
moved into
position over a layer of boxes and the hands 40 and 70 are retracted or closed
around the layer.
The sets 86, 96, and 100 of vacuum devices are brought into contact with the
top surface of the
layer of boxes such that the vacuum devices are aligned along a seam 105
between the boxes.
The compression force exerted by the hands in conjunction with the vacuum grip
provided along
the seam enables the end effector 20 to grasp an entire layer of low friction
boxes without
damage or fall-out problems. Surprisingly, the inventor has discovered that
application of
vacuum grip along the seam 105 in the layer of boxes is effective to create a
vacuum seal
between the cup and the boxes. This finding is contrary to standard vacuum
gripping techniques
which teach that vacuum should be applied away from seams in layers of boxes
and usually at
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the center of a box face. The inventor believes that application of vacuum
along the seams
between adjacent boxes wrapped in packaging material is effective because the
packaging
material from adjacent boxes stretches and tightly closes the seam between the
boxes permitting
the formation of an appropriate vacuum seal.
Of course, in order to successfully grasp a layer of boxes, the boxes must be
appropriately positioned in a tightly packed configuration such as the layer
79. If one or more
boxes are missing from the layer it is unlikely that a successful pick up
operation can be
executed. To ensure that only full layers of boxes are grasped, the present
invention includes a
plurality of sensors. Sensors 110 and 112 (FIG. 4) are mounted on the plate
84, a sensor 114 is
mounted on the underside of the main body 28, and two sensor 116 and 118 are
mounted on the
plate 94. Each of the sensors 110, 112, 114, 116, and 118 is coupled in data
communication to
the processor 24. Before grasping a layer of boxes, the robot positions the
end effector 20 above
the layer and sweeps across it, so that the sensors can scan the entire layer.
If one of the sensors
finds a gap or hole in the layer, its sends a signal to the processor 24
which, in response, instructs
the robot 20 to move to an alternative station to grasp a layer which may be
available there or
generate an alarm or other signal to indicate that human intervention is
required to properly pack
the layer of boxes to be picked up.
In addition to the above features, the present invention includes a system for
handling slip
sheets. Two slip sheet vacuum assemblies 125 and 130 (FIGS. 2 and 3) are
mounted on the first
and second vacuum plates 84 and 94, respectively. Since the assemblies are
substantially the
same, only the assembly 130 is discussed in detail.
The slip sheet gripper assembly 130 has a mount 132 connected to the plate 94.
First and
second arms 134 and 136 are pivotally connected to the mount 132. An actuator
140 is coupled
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between the arms and operable to move them between a raised position R and a
lowered position
L. The arm 134 has a leg 142 with a vacuum/blow-off mechanism 144 and a vacuum
cup 146.
A slip sheet sensor 148 is mounted to the leg 142 adjacent to the cup 146.
Similarly, the arm 136
has a leg 152, a vacuum/blow-off mechanism 153, and vacuum cup 154.
The operation of the two assemblies 125 and 130 is synchronized such that they
are
raised and lowered together. The assemblies are lowered and the end effector
is moved to a
stack of slip sheets to grasp a single sheet using vacuum applied through the
vacuum cups.
Sheets are released by a blow-off action and positioned between layers of
boxes. Of course, the
assemblies 125 and 130 may also be used to place bottom and cap sheets on a
stack.
The sensor 148 on the assembly 130 and a sensor 155 (FIG. 4) on the assembly
125 are
coupled in data communication to the processor 24 through data links (not
shown). Should one
or both of the assemblies lose grip of a slip sheet, a signal from one or both
of the sensors 148
and 155, as the case may, is sent to the processor 24 which responds by having
the robot pick up
another slip sheet or indicate to a display or other device (not shown) that
human intervention is
necessary to correct the situation.
Another embodiment of the present invention in shown in FIGS. 6-10. The
figures show
an end effector 200 which is similar to the end effector 20, but equipped with
hands that are able
to selectively grasp and release rows of boxes. Particularly, the end effector
200 has a first hand
205 which is coupled to the main body of the end effector 200 in the same
manner as the hands
40 and 70 are coupled to the main body 28 of the end effector 20. Thus, the
hand 205 is movable
between a first, retracted position HEp and a second, retracted position HEB.
The first hand 205 includes a main support 210 having a plurality of fingers
attached
thereto. Fingers 212 and 214 are readily removable from the support 210 by
loosening
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removable nuts 216 and 218. A third finger 220 is fastened in place with
standard nuts 220. A
fourth finger 226 is pivotally mounted to the support 210 by a link 228 and is
coupled to an
actuator 230. The actuator 230 is pivotally mounted in a bracket 232 which
sits on the main
support 210 and is operable to move the finger 226 between an open position OP
and a closed
position CP (FIGS. 9 and 10).
The actuator 230 works with a toggle assembly 235 having a first arm 236 and a
second
arm 237 (FIG. 9 and 10). The arms 236 and 237 are connected to drive shaft 239
from the
actuator 230. The arm 237 is coupled to the finger 226 through the link 228.
The drive shaft 239
may be driven between an extended position TE to a retracted position TR. When
in the position
TE, the arms 235 and 237 are maintained in horizontal positions and the finger
226 is held in a
vertical position FV, which corresponds to the closed position CP. When the
shaft is moved to
the position TR, the arms 235 and 237 are pulled up and the finger is moved to
an angled
position FA which corresponds to the open position OP.
Each finger 212, 214, 220, and 226 may consist of a plate of relatively rigid
material and
have a thickness of approximately'/4 of an inch. Preferably, each plate is
straight and square
(i.e., at right angles). Materials with a modulus of elasticity of l Opsi such
as aluminum are
suitable for use in this embodiment of the invention. Like the fingers used in
the end effector 20,
the fingers 212, 214, 220, and 226 may be coated with a layer of rubber or
similar material that
exhibits stickiness. Suitable materials include gum or neoprene rubber. It has
been found that
materials having a durometer in the range of about 30 soft to of about 50 soft
are useful for the
purposes of the present invention.
The end effector 220 includes a second hand 275, which is identical to the
hand 205. It
will, therefore, not be described in detail. However, it should be noted that
for each hand 205,
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275, the number and configuration of fingers could take multiple forms. For
example, more than
one pivotable finger could be mounted on the main support and the location
could be varied
depending on the load to be grasped. Further, fingers with various cut-outs
could be placed on
the hand at positions as desired, again depending on the load to be handled.
For example, FIG. 6
illustrates fingers 220 and 226 with lateral cut outs 280. Of course, all the
fingers or different
fingers may be equipped with such cut-outs as needed.
The features of the end effector 200 discussed above, including the pivoting
action of the
fourth finger, allow it to create a stack of unevenly sized rows of boxes,
such as the stack 300 in
FIG. 12. Each layer 302 in stack 300 consists of two rows 304 and 306 of a
first size and two
rows 308 and 310 of a second size. Using the end effector 200, equipped with
the hands 205 and
275, the center two rows are placed in each layer 302 and then the outer two
rows 308 and 310
and placed on each layer. As should be apparent, the provision of a pivotable
finger (such as the
finger 226) on the hands 205 and 275 allows the end effector 200 to release
individual rows of
boxes so that such stacks can be created. Generally, the outside fingers 212
and 214 are removed
so as not to interfere with handling individual rows or less than a full layer
of boxes. The ability
to create these types of stacks is important in situations where the
dimensions of the individual
containers making up the rows is such that a square layer of containers can
not be created or the
boxes cannot be positioned in such a way that it would be effective to grasp
an entire layer of
containers with an end effector configured such as the end effector 20.
Another aspect of the present invention is shown in FIG. 8. If needed, the end
effector
200 and, even though not shown, the end effector 20 may be equipped with
auxiliary suction
devices such as the devices 350, 352, 354, and 355 in FIG. 8. The devices are
coupled to the
main body of the end effector and positioned such that when the end effector
grasps a layer of
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boxes they provide vacuum at additional seams in the layer grasped. Thus,
additional grip
support is provided beyond that given by the center row of vacuum devices.
As can be seen from the above, the present invention provides a robot gripper
capable of
grasping and manipulating boxes and similar items wrapped in packaging
material. Its hands
have unique features including fingers designed to accommodate wrapped items
and utilizes a
counter-intuitive vacuum assist system to maintain grip on an entire layer of
boxes. Further,
although the invention has been described by reference to the drawings and
examples contained
herein, it is not limited thereby and encompasses everything within the scope
of the following
claims.
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